The present invention relates to circuits, devices and apparatuses for dimming electrical lighting. More particularly, this invention relates to dimming circuits, devices and apparatuses for use with energy saving lamps or compact fluorescent lamps.
Compact fluorescent lamps, more commonly known as energy saving lamps, are widely used nowadays because of the many advantages including a high power efficiency and a long operating life.
It is well known that fluorescent lamps appear as a variable or non-linear load to a power supply depending on the lamp operating modes. In order to supply an appropriate amount of current for proper lamp operation regardless of the instantaneous operating mode, a ballast is always provided between the main power supply and the fluorescent lamp. In general, a ballast must provide a required high starting voltage and current as well as limiting the current which can pass through the lamp during steady-state operation.
In many occasions, it is desirable to be able to dim the electric lightings. However, dimming of fluorescent lamps has been historically difficult and requires complicated circuit arrangements and topologies. A typical type of dimmer for fluorescent lamps is provided by periodically blocking the supply voltage to the light source by clipping a portion of the AC sinusoidal by reference to the phase angle of the AC power light input. These dimmers are commonly referred to as xe2x80x9cphase control dimmersxe2x80x9d which can be a forward phase dimmer or a reverse phase dimmer. A forward phase dimmer usually utilizes a thyristor, such as a silicon controlled rectifier (SCR) or, more commonly, a triac as an electronic blocking device or switch. On the other hand, a reverse phase dimmer allows the passage of the portion of the half-cycle of the AC line input immediately after the zero crossing of the AC line and blocks the portion of the half-cycle before the zero-crossing. In both types, the portion or angle of the half-cycle which is to be blocked is adjustable to control dimming. A major shortcoming of this phase control dimmers is that zero crossing detection is a pre-requisite of operation.
However, in circumstances in which the detection of zero crossing is difficult, for example, in the case of a fluorescent lamp with an electronic capacitive ballast, such phase control dimmers will not be suitable. Furthermore, because of the difficulty in dimming fluorescent lamps, most commercially available dimmable fluorescent lamps have the dimmer integrated with the ballast which means remote dimming of conventional fluorescent lamps with integrated electronic ballasts at remote switching locations such as wall-mounted switches is not possible. Hence, it would be highly desirable if there can be provided a simple dimmer or dimmer circuit which can be remotely installed from a compact fluorescent lamp so that dimming of the lamps can be controlled at locations remote from the lamps. In order that the dimmers can be installed at locations reserved for, or already installed with, conventional standard wall sockets, it would be highly desirable if the dimming circuitry is simple enough to be received within a confined space commonly allowed for a standard wall socket. Furthermore, it will be highly desirable if there can be provided a two-wire dimmer for a compact fluorescent lamp so that the dimmer can be retro-fittable without the need of additional wiring.
It is therefore an object of the present invention to provide improved circuits, devices and apparatuses for dimming a fluorescent lamp, especially a compact fluorescent lamp or an energy saving lamp. In particular, it will be an object of the present invention to provide simple dimmers for use with a compact fluorescent lamp which can be remotely located from the fluorescent lamp. It is also another object of the present invention to provide simple circuitry which can be utilized to dim a compact fluorescent lamp without the need of zero-crossing detection of the AC input line to alleviate the complicated circuitry required for such detection. Furthermore, it is an object of the present invention to provide a two-wire dimmer for a fluorescent lamp or the like. It is a least an object of the present invention to provide the public with the choice of a dimmer which can be used with a fluorescent lamp, such as compact fluorescent lamp or an energy saving lamp.
According to a first aspect of the present invention, there is provided a dimming device including an input terminal for connecting to an alternate current power supply, an output terminal for connecting to a load, and a switched mode power supply wherein said switched mode power supply includes an electronic switching means with first and second switch terminals, switching control means, inductive means and capacitive means, said inductive means being generally connected in series with said switching terminals of said switching means and said capacitive means being connected generally in parallel with the series connection including said switching device and said inductive means and wherein the switching frequency of said electronic switching means is controllable and variable by said switching control means.
According to a second aspect of the present invention, there is provided a two-terminal dimming device for a compact fluorescent lamp including a switched mode power supply which includes rectifying means, electronic switching means, an inductive member, a capacitive member and a switching control means, said rectifying means is connected to said switching means via said inductive member, said capacitive member is connected generally in parallel to the series connection of said inductive member and said switching means, and said switching control means provides switching signals to said switching means, the frequency of said switching signals is substantially higher than that of the input power.
According to a third aspect of the present invention, there is provided a dimming device including an input terminal for connecting to an alternate current power supply, an output terminal for connecting to a load, and a switched mode power supply arrangement, said switched mode power supply includes an electronic switching means with first and second switch terminals, switching control means, an inductor and a capacitor, said first and second terminals of said electronic switching means, said inductor and said capacitor being arranged in a circuit loop, wherein the switching frequency of said electronic switching means is controllable and variable by said switching control means.
Preferably, an inductor is connected between the output of said switched mode power supply and said output terminal of said dimming device.
Preferably, said switching frequency of said electronic switching means is substantially higher than that of the frequency of said alternate current power supply.
Preferably, switching control means include a micro-controller or micro-processor sending out pulse-width modulated (PWM) switching signals.
Preferably, said switching frequency of said switching means is between 1 kHz and 50 kHz.
Preferably, wherein said electronic switching device can be a bipolar transistor, a MOSFET or an IGBT.
Preferably, said inductive means include an inductor and said capacitive means include a capacitor.
Preferably, further including rectifying means for providing rectified power supply to said switching means.
Preferably, an additional inductive member is connected at the output of said device.
Preferably, said series connection of said switching device and said inductive means is further connected in series with a rectifying means, said capacitive means being connected in parallel with the series connection of said switching device, said inductive means and said rectifying means.
Preferably, said switching signals include a pulse train of signals with levels corresponding to xe2x80x9cONxe2x80x9d or xe2x80x9cOFFxe2x80x9d switching states and that the relative duration of the xe2x80x9cONxe2x80x9d and xe2x80x9cOFFxe2x80x9d pulses can be gradually varied.
Preferably, said series connection of said switching device and said inductive means is further connected in series with a rectifying means, said capacitive means being connected in parallel with the series connection of said switching device, said inductive means and said rectifying means.
Preferably, one terminal of the dimming device is for connecting to the AC mains and the other terminal is for connecting to the electronic ballast of a compact fluorescent lamp.
According to a third aspect of the present invention, there is provided a lighting system including the above-mentioned dimming device and a compact fluorescent lamp.
Preferably, the position of said dimming device is independent of that of said compact fluorescent lamp.
According to a fourth aspect of the present invention, there is provided a lighting arrangement including a compact fluorescent lamp with an electronic ballast and a dimming device of the above characteristics.